Skirts for hovercraft

ABSTRACT

This invention relates to skirts for hovercraft, and the object thereof is the avoidance of the bailing effect or accumulation of water in the space defined by the skirt when the craft is moving. Most hovercraft skirts have a truncated conical shape in section, the walls thereof converging inwardly in the downwards direction. The invention proposes to cut away certain areas of the skirt and these areas are bridged by wall members or pockets which extend outwardly from the skirt and are of part-conical shape with the apex uppermost in the operating condition of the craft. The wall member or pocket may be reinforced by a metal strip which may be folded concertina-wise so as to expand on the application of internal pressure and it may furthermore be cut away at the apex to provide an escape route for water, also to assist in the relief of built up pressure. The wall members or pockets may be made from a material less mechanically resistant than that of the skirt or may be attached to the skirt by connection means that give way upon the application of excess pressure. Only one such wall member or pocket may be provided but, where a plurality of them is present, they are arranged symmetrically about the longitudinal axis of the skirt, i.e. the hovercraft, in the operating condition.

Unite States Patent [191 Raux [ SKIRTS FOR HOVERCRAFT [75] Inventor: Raymond Henri Raux, Maisons Laffitte, France [73] Assignee: Pneumatiques, Caoutchouc Manufacture et Plastiques Kleber-Colombes, Colombes, France [22] Filed: Feb. 7, 1972 [21] Appl. No.: 223,939

[30] Foreign Application Priority Data Feb. 12,1971 France ..7104934 [52] US. Cl. 114/67 A, 180/128 [51] Int. Cl. B60v 3/06 [58] Field of Search 180/116, 127, 128; 114/67 A, 67 R [56] References Cited UNITED STATES PATENTS 3,252,536 5/1966 Jones 180/128 Primary Examiner-Duane A. Reger Assistant Examiner-Paul E. Sauberer AttorneyJoseph F. Brisebois et al.

[57] ABSTRACT This invention relates to skirts for hovercraft, and the object thereof is the avoidance of the bailing effect or accumulation of water in the space defined by the skirt when the craft is moving. Most hovercraft skirts have a truncated conical shape in section, the walls thereof converging inwardly in the downwards direction. The invention proposes to cut away certain areas of the skirt and these areas are bridges by wall members or pockets which extend outwardly from the skirt and are of part-conical shape with the apex uppermost in the operating condition of the craft. The wall member or pocket may be reinforced by a metal strip which may be folded concertina-wise so as to expand on the application of internal pressure and it may furthermore be cut away at the apex to provide an escape route for water, also to assist in the relief of built up pressure. The wall members or pockets may be made from a material less mechanically resistant than that of the skirt or may be attached to the skirt by connection means that give way upon the application of excess pressure. Only one such wall member or pocket may be provided but, where a plurality of them is present, they are arranged symmetrically about the longitudinal axis of the skirt, i.e. the hovercraft, in the operating condition.

11 Claims, 7 Drawing Figures SKIRTS FOR HOVERCRAFT The present invention relates to hovercraft, i.e., craft supported by reaction thrust against the ground or water, and particularly to the skirts for such craft which depend from the hull and define a space in which the reaction thrust is concentrated.

Hovercraft skirts usually have the shape of a downwardly converging truncated cone, i.e., a truncated cone the apex of which is located beneath the craft: this shape has been chosen and is substantially universally used because it confers a good degree of stability to the craft.

Nevertheless this shape, due to the inward inclination of the skirt, suffers from the serious drawback of opposing the outlet of that which is in the space defined by the skirt. Where the craft is operated on water, then of course it is water that is present in this space. When the craft operates, the mass of water tends constantly to increase and accumulates in this space in the rear part of the craft and is entrained by the skirt; this phenomenon is known under the name of bailing. Moreover, it frequently happens that the stresses to which the skirt is subjected on account of the accumulated water become such that the skirt tears; this is obviously harmful to the good operation of the craft.

In order to remedy this drawback, skirts have been produced having a rear part, i.e., that part of the skirt situated at the rear of the craft, which is made as two separate members interconnected by elastic stretchers. In certain cases, these two members overlap one another and, in other cases, they do not; however, whether there is overlap or not, this solution is not satisfactory as experience has shown. In fact, if the two ends do not overlap, there is permanently at the base of the skirt a loss of air which, therefore, cannot be used in supporting the craft and, if the ends do overlap, it frequently occurs that the skirts are damaged as a consequence of bailing. This is due to the fact that there is elongation of the stretchers only when large stresses are exerted and that this elongation, always slight, only causes negligible alteration of the conicity of the skirt and of its inclination inwardly; in other words, the shape of the skirt is not sufficiently changed to enable evacuation of the water tending to accumulate by bailing.

Thus, it is a primary object of the invention to provide a hovercraft skirt which affords an efficient elimination of the water accumulated by the bailing action hereinabove referred to.

According to the invention, the lower part of the skirt is cut away in at least one area, said area being covered by a wall member secured to theouter face of said skirt along the outer edges of said cut-away area. Preferably, the wall member has a conical or truncated conical shape, the apex of which is uppermost, when the craft is in operation.

Advantageously the wall members are removable to facilitate replacement thereof; this enables the skirt itself to be protected by forming a preferential breaking zone if the stresses are too great.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings which show certain embodiments thereof by way of example, and in which:

FIG. A is a side view of a hovercraft in operation, partly in section,

FIG. 1 shows a perspective view of the rear part of a skirt according to the invention, e.g., for a craft such as that shown in FIG. A,

FIG. 2 shows a vertical section along the line II--II of FIG. 1,

FIG. 3a shows a view in section along the line III-III of FIG. 1,

FIG. 3b shows an identical view to that of FIG. 3a, when the craft is not operating,

FIG. 4 shows a horizontal section of another embodiment of the wall member or pocket positioned in front of the cut-away area, and

FIG. 5 shows a view of one part of another embodiment of skirt.

Referring now to the drawings, FIG. A shows a general view of a hovercraft at 1 with a downwardly tapering skirt of axial length H, the taper angle of the truncated conical shape being represented by When operating on water, there is entrapped within the space defined by the skirt a volume of water indicated at 2., which volume tends to increase by a bailing action as the craft moves, as hereinabove referred to.

FIG. 2 shows a perspective view of the skirt rear portion, with the general reference 10. The skirt 10 may be of any suitable construction; it may be for example formed by a woven material covered with rubber.

At the rear part of the craft, the lower edge of the skirt 10 is provided with one or more cut-away areas having the general shape of a triangle or isosceles trapezium; preferably, the ratios of the base 1 (FIG. 1) of the triangle or-trapezium and its height h to the axial height H (FIGS. A and 2) of the skirt, corresponding to the length of the generatrix of the formed truncated cone, are between 0.6 and 0.9. The number of cutaway areas depends on the inclination and axial height H of the skirt, the actual construction of the craft and conditions under which the latter is to be used; in a general manner, the skirt will include an increased number of cut-away areas as the volume of water accumulated by bailing is itself expected to increase. If the skirt has only one cut-away area, the latter would be situated at the rear part of the craft along the longitudinal axis of I the latter; if the skirt has more than one cut-away area,

the assembly of such areas is preferably symmetrical about the longitudinal axis of the craft.

A supple wall member or pocket 11 is added in front of each cut-away area and this wall member or pocket may be made for example from cloth covered with rubher which is fixed to the skirt close to the edges of the cut part and the width of which is greater than that of the cutaway area so as to form under the effect of over pressure of the air contained in the enclosure defined by the skirt, a conical part, usually a conical sector which is limited by the edges of the cut-away area. At the positions of this cut-away area, the skirt 10 is replaced by the wall member or pocket 11, the width of which is selected so that the angle formed by its central part with the plane of the cut-away area (FIG. 2) is slightly less thanthe angle formed by the skirt with the vertical (FIG. 2); thus, at the positions of the cutaway areas, the wall member is inclined to the vertical by an angle less than the angle of inclination of the remainder of the skirt, which enables continuous elimination of the water which accumulates by means of bailing and thus lessens the danger that a large quantity of water will cause high stresses to cause tearing of the skirt.

is provided with a skirt of height H 1.4 m inclined to the vertical by an angle [3 of 1230; the skirt has at its rear end two cut-away areas symmetrical with respect to the axis of the craft and having the shape of isosceles triangles of height 1.1 m and base 1.2 m covered by wall members or pockets made from rubberised cloth, the central part of which makes an angle oz of with the skirt. Thus, at the areas where the skirt has been cut away, the central zone of the wall member makes with the vertical an angle which is only 230; although in this particular case the wall member is further inclined towards the centre of the craft which is favourable for good operation thereof, this inclination is sufficiently small to enable elimination of the accumulated water by bailing.

In order to prevent the edges of the cut-away area from diverging, the wall members or pockets 11 connect them together; preferably, these members or pocketsare elastic and thus stretch to absorb certain abnormal stresses and also to tend continuously to draw the edges of the cut-away area together.

a The members 11 forming pockets on the skirt of the craft are fixed on the edges of the cut-away area by any suitable means. They may, for example, be fixed by vulcanisation of the rubber; they may also be fixed by purely mechanical connecting means such as riveting, or by nuts and bolts, either of which expedients have the advantage of making the pockets readily replaceable. This solution becomes particularly advantageous when in order to form a protection for the actual skirt against possible tears resulting from excess stresses, the wall members or. pockets 11 are used to offer a preferential breaking zone. To this end, the members or pockets 11 are either made to have a mechanical'resisreached.

.The skirt 14 shown in FIG. 5 represents the embodiment of another embodiment in which the wall member or pocket which is fixed in front of its cut-away area preserves its geometrical shape even when the enclosure represented by the skirt is not over pressurised by the volume of water in space defined thereby. To this end, transverse mechanical resistance elements 15 are applied to the wall member or pocket and are securely connected thereto. These elements may be metal ca bles or'e'ven strips or rods made from a spring steel, being advantageously pre-shaped in bellows or concertina form during manufacture, whereby when they take up their initial shape, they draw the edges of the cutaway area together when this proves necessary.

Moreover, in the manner also to facilitate evacuation of the water held in suspension in the air cushion within the skirt, the upper part of the cone formed'by the added wall member or pocket may, as in this embodiment, be cut off at 16. Thus, by means of this orifice which opens out into the open air a suction towards the outside is created which further facilitates evacuation of the water; the orifice 16 thus made is of a sufficiently small dimension not to affect operation of the hovercraft.

I claim:

1. A flexible skirt for a hovercraft for forming-an enclosure in the shape of a truncated cone beneath the hull of said craft and directed towards the bearing surface thereof, said skirt being cut away in at least one area in the lower part of said skirt, said cut-away area being covered by a wall member secured to the outer face of said skirt along the edges of said cut-away area.

2. A skirt according to claim I, wherein said wall member is elastic to pull the edges of said cut-away area together.

3. A skirt according to claim 1, wherein a plurality of said wall members each cover a cut-away area, and wherein said wall members are symmetrical about the longitudinal axis of said skirt when in operational association with a hovercraft.

4. A skirt according to claim 1, wherein said wall member has a shape which is at least part of a cone whose apex is uppermost in the operating condition of the hovercraft.

5. A skirt according to claim 4, wherein said wall member is provided with transverse mechanical resistance elements secured thereto.

6. A skirt according to claim 5, wherein said transverse elements are of metal.

7. A skirt according to claim 1, wherein said wall member is securely fixed to said skirt.

8. A skirt according to claim 1, wherein the mechanical resistance of said wall member is less than that of the remaining part of said skirt.

9. A skirt according to claim 8, wherein said wall member is attached to said skirt by means which yield under a predetermined applied stress.

10. A skirt according to claim 4, wherein the upper part of said at least part-conical shape is cut away to allow the interior of said skirt to communicate with the open air. 1

11. In combination, a hovercraft and a skirt accord ing to claim 1.

I I. l i 

1. A flexible skirt for a hovercraft for forming an enclosure in the shape of a truncated cone beneath the hull of said craft and directed towards the bearing surface thereof, said skirt being cut away in at least one area in the lower part of said skirt, said cut-away area being covered by a wall member secured to the outer face of said skirt along the edges of said cut-away area.
 2. A skirt according to claim 1, wherein said wall member is elastic to pull the edges of said cut-away area together.
 3. A skirt according to claim 1, wherein a plurality of said wall members each cover a cut-away area, and wherein said wall members are symmetrical about the longitudinal axis of said skirt when in operational association with a hovercraft.
 4. A skirt according to claim 1, wherein said wall member has a shape which is at least part of a cone whose apex is uppermost in the operating condition of the hovercraft.
 5. A skirt according to claim 4, wherein said wall member is provided with transverse mechanical resistance elements secured thereto.
 6. A skirt according to claim 5, wherein said transverse elements are of metal.
 7. A skirt according to claim 1, wherein said wall member is securely fixed to said skirt.
 8. A skirt according to claim 1, wherein the mechanical resistance of said wall member is less than that of the remaining part of said skirt.
 9. A skirt according to claim 8, wherein said wall member is attached to said skirt by means which yield under a predetermined applied stress.
 10. A skirt according to claim 4, wherein the upper part of said at least part-conical shape is cut away to allow the interior of said skirt to communicate with the open air.
 11. In combination, a hovercraft and a skirt according to claim 